1. Field of the Invention
The invention relates to systems for providing a panoramic view of an environment. The invention is related to submarine masts, particularly of the non-rotating, non-hull penetrating type.
2. Description of the Prior Art
Traditionally, submarines include a rotary periscope mast that provides a continuous 360xc2x0 scan or pan of the outside environment of the submarine. Such periscopes require a marine rotating mast seal which is difficult to construct and maintain. Present day submarines also include a fixed, non-rotating, non-hull penetrating intelligence and signal gathering mast containing integrated electronic intelligence gathering systems. In use, such an intelligence gathering mast normally does not permit the simultaneous use of the traditional periscope mast. The intelligence or signal gathering mast may be required to operate over many hours, during which time there cannot be a simultaneous use of the periscope mast requiring above water exposure. This is because the signal gathering capability of the intelligence gathering mast is compromised by the metals contained in the periscope mast which distort the weak electromagnetic fields or signals that the intelligence gathering mast is endeavoring to detect. It is appreciated, however, that for threat warning purposes and general surveillance, a panoramic system is desired that pans through 360xc2x0 permitting an operator to obtain a complete visual panoramic search of the outside environment surrounding the submarine while the traditional optical rotary periscope is unusable. It is furthermore desirable to include, if possible, such a visual panoramic scanning system within the intelligence gathering mast.
The intelligence gathering mast is required to be small in visual and radar cross-section and as a result tends to be densely occupied with components such as antennas, and the like. In such a mast the central or axial space thereof tends to be crowded with equipment, which space may otherwise have been utilized for the visual panning system. In such a mast only extremely limited off-center and off-axial, relatively remote internal space is available for the visual system. Known panning systems tend to be large and heavy, requiring components to be axially located within a mast. Such prior art panning systems additionally tend to include large numbers of moving parts, thereby reducing the reliability of the system and increasing the required maintenance thereof. It is appreciated that the inside volume of an intelligence gathering mast is extremely sensitive to the placement, volume, composition and type of metallic components disposed therein. Known systems which may be utilized to add visual capability to an intelligence gathering mast include numerous metallic parts and electronic components that cannot be relocated to a remote space.
A non-rotary visual mast design includes panoramic windows surrounding the mast forming a section thereof. A centrally or axially located camera is utilized to pan through the panoramic windows as desired through 360xc2x0. Such a system suffers from the disadvantages discussed above with respect to prior art panning systems and, additionally, could not be incorporated into the tightly packed integrated electronic surveillance mast where the central and axial locations are unavailable.
Another non-rotary visual capability mast design is to include a plurality of windows circumferentially around the mast, each providing a sufficiently wide angle field of view to respective fixed cameras so as to provide a full 360xc2x0 scene. Such an arrangement requires multiple cameras and complex pan processing to provide the desired result. The multiple camera design tends to be excessively bulky and expensive, as well as requiring undesirably large power consumption and dissipation. Furthermore, plural video data cables from the cameras overburden the limited space of the mast.
Thus it is appreciated, that conventional methods of forming visual surveillance over 360xc2x0 have utilized scanning television cameras with a single monitor or multiple overlapping field of view cameras with multiple monitors. Both of these techniques are undesirable, especially for military applications, because of the presence of moving parts in the former case and the large size and complexity in the latter case.
The above-described disadvantages of the prior art are overcome by a panoramic visual system comprising a plurality of lenses disposed about the periphery of a structure, each lens providing a field of view that at least abuts the fields of view of the lenses adjacent thereto. Thus, the lenses provide a 360xc2x0 coverage of the scene. The lenses image the respective fields of view onto the ends of a plurality of respective image relays. The other ends of the image relays are disposed adjacent each other in a closed arrangement, with adjacent relayed images corresponding to adjacent lenses. The closed arrangement of adjacent relayed images forms a continuous panoramic replica of the 360xc2x0 scene viewed by the lenses. Thus, a continuous pan of the environment surrounding the structure can be accessed by a continuous rotary scan of the relayed images assembled into the closed arrangement.
Preferably, a rotating mirror or prism directs the scanned panoramic image through a relay lens into a television camera. An image intensifier may be utilized at the input of the camera to increase the dynamic range of the system and to provide automatic light level control. Means are included to compensate for the rotation imparted to the image impinging on the camera by the rotating mirror or prism. Preferably, a derotating prism geared to the image directing mirror or prism and disposed in the path of the rotating image is utilized for this purpose.
For purposes of integration of the visual system into an intelligence gathering mast, the lenses, image relays, and all attaching hardware are, preferably, constructed of dielectric materials.